Foam material particles based on long-chain polyamides

ABSTRACT

Foam particles that have a bulk density below 300 kg/m 3  and are based on polyamides, including 85% to 100% by weight of at least one copolyamide obtainable by polymerizing the following components:
         (A) 15% to 84% by weight of at least one lactam,   (B) 16% to 85% by weight of a monomer mixture (M) including the following components:
           (B1) at least one C 32 -C 40  dimer acid and   (B2) at least one C 4 -C 12  diamine,   wherein the monomer mixture (M) includes in the range from 45 to 55 mol % of component (B1) and in the range from 45 to 55 mol % of component (B2), based on the total molar amount of the monomer mixture (M), and the sum total of the components of (A) and (B) is 100% by weight, and processes for production thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase Application of InternationalPatent Application No. PCT/EP2019/068716, filed Jul. 11, 2019, whichclaims the benefit of priority to European Patent Application No.18184128.9, filed Jul. 18, 2018, the entire contents of each of whichare hereby incorporated by reference herein.

DESCRIPTION

The invention relates to foam particles based on polyamides, comprising85% to 100% by weight of at least one long chain copolyamide, and toprocesses for production thereof.

WO 2011/134996 describes expandable polyamide-based pellets that can befoamed in a prefoamer to give expanded polyamides and are suitable forproduction of a particle foam for use in the automotive industry,aviation industry, building industry, packaging industry, sports andleisure industry, in transport and/or in construction.

US 2007/036967 describes, inter alia, rigid expanded polyamide pelletshaving a density of 600 kg/m³ that are said to be obtained by extrusionof a mixture of nylon-6 pellets and polycarbonate pellets in a twinscrew extruder, with subsequent underwater pelletization.

JP7179645 describes cylindrical high-density polyamide foam particlesthat are obtained by melt extrusion of a polyamide containing 1-5 partsby weight of water, followed by strand pelletization.

WO 2014/198779 describes a process for producing expanded pellets from athermoplastic elastomer having elongation at break of more than 100%measured to DIN EN ISO 527-2, comprising the steps of: (a) pressing thepolymer melt comprising a blowing agent through a perforated diskcontrolled to a temperature between 150° C. and 280° C. and into apelletizing chamber, b) using a cutting device to comminute the polymermelt pressed through the perforated disk into individual expandingpellets, c) discharging the pellets from the pelletizing chamber using aliquid stream, wherein the blowing agent comprises CO₂ or N₂ or acombination of CO₂ and N₂ and the amount of blowing agent in the polymermelt comprising blowing agent is in the range from 0.5% to 2% by weight,and wherein the pelletizing chamber is traversed by a stream of liquidwhich is controlled to a temperature between 150° C. and 280° C. and thepressure of which is from 0.1 bar to 20 bar above ambient pressure, thepressure and temperature for the liquid in the pelletizing chamber andalso the temperature for the perforated disk being chosen such that thepellets are expanded in the pressurized liquid by the blowing agent theycontain so as to produce expanded pellets having an uninterrupted skin.One thermoplastic elastomer used is a polyether copolyamide (PEBA).

WO 2017/013510 describes foamed materials having improved solventresistance and a density of 40 to 700 kg/m³, formed from 50-90% byweight of semicrystalline polymer and 10-50% by weight of apolyphenylene ether. Semicrystalline polymers used may be polyamides,polyesters and polyolefins. The foams may be obtained by impregnatingthe polymer melt with a blowing agent in the extruder.

WO 2016/030333 describes, inter alia, the production of expandedparticles based on polyether-block-amides (PEBA) and nylon-12 byextrusion and impregnation of a polymer melt with CO₂, followed byunderwater pelletization. The amorphous fractions are increased byadding a chain extender, for example a styrene acrylate with reactiveepoxy groups.

WO 2018/050487 describes a polymer film comprising at least onecopolyamide, wherein the copolyamide has been prepared by polymerizing15% to 84% by weight of at least one lactam and 16% to 85% by weight ofa monomer mixture comprising at least one C₃₂-C₄₀ dimer acid and atleast one C₄-C₁₂ diamine.

Owing to their high chemical stability, thermal stability and stresscracking resistance, semicrystalline polymers such as polyamides orpolyesters are of interest for particle foams. In the case ofsemicrystalline polymers, however, the processing window for foaming togive foams having homogeneous foam structure and mechanical propertiesis too small. The addition of additives such as chain extenders and/orcrosslinkers can have an adverse effect on the mechanical properties.The addition of fillers to regulate melt viscosity generally leads tohigh densities and to embrittlement of the foams.

It was therefore an object of the present invention to provide foamparticles based on polyamides and processes for production thereof,which are especially processible even without additives, especiallywithout chain extenders or high proportions of fillers, to give foamshaving low density and good mechanical properties.

The object was achieved by foam particles that have a bulk density below300 kg/m³ and are based on polyamides, comprising 85% to 100% by weightof at least one copolyamide obtainable by polymerizing the followingcomponents:

-   -   (A) 15% to 84% by weight of at least one lactam,    -   (B) 16% to 85% by weight of a monomer mixture (M) comprising the        following components:        -   (B1) at least one C₃₂-C₄₀ dimer acid and        -   (B2) at least one C₄-C₁₂ diamine, wherein the monomer            mixture (M) comprises in the range from 45 to 55 mol % of            component        -   (B1) and in the range from 45 to 55 mol % of component (B2),            based on the total molar amount of the monomer mixture (M),            and the sum total of the components of (A) and (B) is 100%            by weight.

Preferably, the foam particles consist of 85% to 100% by weight of thecopolyamide described hereinafter and 0% to 15% by weight of additives,such as nucleating agents, dyes, pigments, fillers, flame retardants,flame retardant synergists, antistats, stabilizers (for examplehydrolysis stabilizers), surface-active substances, plasticizers andinfrared opacifiers.

More preferably, the foam particles consist of 98% to 99.9% by weight ofthe copolyamide described hereinafter and 0.1% to 2% by weight of anucleating agent, especially talc.

The foam particles have a bulk density below 300 kg/m³ preferably in therange from 30 to 250 kg/m³, more preferably in the range from 40 to 200kg/m³ and most preferably in the range from 80 to 150 kg/m³.

Copolyamide

According to the invention, the copolyamide is prepared by polymerizingthe following components:

-   -   (A) 15% to 84% by weight of at least one lactam,    -   (B) 16% to 85% by weight of a monomer mixture (M) comprising the        following components:        -   (B1) at least one C₃₂-C₄₀ dimer acid and        -   (B2) at least one C₄-C₁₂ diamine,    -   wherein the monomer mixture (M) comprises in the range from 45        to 55 mol % of component (B1) and in the range from 45 to 55 mol        % of component (B2), based on the total molar amount of the        monomer mixture (M), and the sum total of the components of (A)        and (B) is 100% by weight.

The copolyamide has preferably been prepared by polymerizing from 40% to83% by weight of component (A) and 17% to 60% by weight of component(B), more preferably from 60% to 80% by weight of component (A) and 20%to 40% by weight of component (B), where the sum total of components (A)and (B) is 100% by weight.

The polymerization of components (A) and (B) can take place in thepresence of a catalyst. Preferred catalysts are phosphorus compounds,for example sodium hypophosphite, phosphorous acid, triphenylphosphineor triphenyl phosphite.

The polymerization of components (A) and (B) forms the copolyamide,which therefore comprises structural units derived from component (A)and structural units derived from component (B). Structural unitsderived from component (B) comprise structural units derived fromcomponents (B1) and (B2) and, optionally, from component (B3).

The copolyamide is preferably a random copolymer.

In general, the copolyamide has a glass transition temperature (T_(g))in the range from 20 to 50° C., preferably in the range from 23 to 47°C. and especially preferably in the range from 25 to 45° C., determinedto ISO 11357-2:2014.

In general, the copolyamide has a melting temperature in the range from150 to 210° C., preferably in the range from 160 to 205° C. andespecially preferably in the range from 160 to 200° C., determined toISO 11357-2:2014.

The copolyamide generally has a viscosity number (VN) in the range from150 to 300 ml/g, preferably in the range from 160 to 290 ml/g and morepreferably in the range from 170 to 280 ml/g, determined in a 0.5% byweight solution of the copolyamide in a mixture ofphenol/o-dichlorobenzene in a weight ratio of 1:1.

Component (A)

According to the invention, component (A) is at least one lactam. In thecontext of the present invention, “lactams” are understood to meancyclic amides having preferably 4 to 12 carbon atoms, more preferably 5to 8 carbon atoms, in the ring.

Suitable lactams are for example selected from the group consisting of3-aminopropanolactam (propio-3-lactam; β-lactam; β-propiolactam),4-aminobutanolactam (butyro-4-lactam; γ-lactam; butyrolactam),aminopentanolactam (2-piperidinone; δ-lactam; δ-valerolactam),6-aminohexanolactam (hexano-6-lactam; ε-lactam; ε-caprolactam),7-aminoheptanolactam (heptano-7-lactam; ζ-lactam; ζ-heptanolactam),8-aminooctanolactam (octano-8-lactam; η-lactam; η-octanolactam),9-aminononanolactam (nonano-9-lactam; θ-lactam; θ-nonanolactam),10-aminodecanolactam (decano-10-lactam; ω-decanolactam),11-aminoundecanolactam (undecano-11-lactam; ω-undecanolactam) and12-aminododecanolactam (dodecano-12-lactam; ω-dodecanolactam).

The lactams may be unsubstituted or at least monosubstituted. If atleast monosubstituted lactams are used, the nitrogen atom and/or thering carbon atoms thereof may bear one, two, or more substituentsselected independently of one another from the group consisting of C₁-to C₁₀-alkyl, C₅- to C₆-cycloalkyl, and C₅- to C₁₀-aryl.

Suitable C₁- to C₁₀-alkyl substituents are, for example, methyl, ethyl,propyl, isopropyl, n-butyl, sec-butyl, and tert-butyl. A suitable C₅- toC₆-cycloalkyl substituent is for example cyclohexyl. Preferred C₅- toC₁₀-aryl substituents are phenyl or anthranyl.

It is preferable to employ unsubstituted lactams, γ-lactam(γ-butyrolactam), δ-lactam (δ-valerolactam) and ε-lactam (ε-caprolactam)being preferred. Particular preference is given to δ-lactam(δ-valerolactam) and ε-lactam (ε-caprolactam), 8-caprolactam beingespecially preferred.

Monomer Mixture (M)

According to the invention, component (B) is a monomer mixture (M). Themonomer mixture (M) comprises components (B1), at least one C₃₂-C₄₀dimer acid, and (B2), at least one C₄-C₁₂ diamine.

The monomer mixture (M) comprises in the range from 45 to 55 mol % ofcomponent (B1) and in 30 the range from 45 to 55 mol % of component(B2), preferably in the range from 47 to 53 mol % of component (B1) andin the range from 47 to 53 mol % of component (B2), more preferably inthe range from 49 to 51 mol % of component (B1) and in the range from 49to 51 mol % of component (B2), based on the total molar amount of themonomer mixture (M).

Component (B) may additionally comprise a component (B3), at least oneC₄-C₂₀ diacid.

When component (B) additionally comprises component (B3), it ispreferable that component (B) comprises in the range from 45 to 54.9 mol% of component (B1), in the range from 45 to 55 mol % of component (B2)and in the range from 0.1 to 10 mol % of component (B3), based in eachcase on the total molar amount of component (B).

When component (B) additionally comprises component (B3), the molarpercentages of components (B1), (B2) and (B3) typically add up to 100mol %.

The monomer mixture (M) may further comprise water.

Component (B1)

According to the invention, component (B1) is at least one C₃₂-C₄₀ dimeracid. In the context of the present invention, “at least one C₃₂-C₄₀dimer acid” means either exactly one C₃₂-C₄₀ dimer acid or a mixture oftwo or more C₃₂-C₄₀ dimer acids. C₃₂-C₄₀ dimer acids can be obtained,for example, by dimerizing unsaturated fatty acids, for exampleunsaturated C₁₆ fatty acids, unsaturated C₁₈ fatty acids and unsaturatedC₂₀ fatty acids.

Component (B1) is especially preferably at least one C₃₆ dimer acid. TheC₃₆ dimer acid is preferably prepared proceeding from unsaturated C₁₈fatty acids. The C₃₆ dimer acid is more preferably prepared proceedingfrom C₁₈ fatty acids selected from the group consisting of petroselicacid ((6Z)-octadeca-6-enoic acid), oleic acid ((9Z)-octadeca-9-enoicacid), elaidic acid ((9E)octadeca-9-enoic acid), vaccenic acid((11E)-octadeca-11-enoic acid) and linoleic acid((9Z,12Z)-octadeca-9,12-dienoic acid). The preparation of component (B1)from unsaturated fatty acids can additionally form trimer acids;residues of unreacted unsaturated fatty acid may also remain.

Preferably in accordance with the invention, component (B1) comprises atmost 0.5% by weight of unreacted unsaturated fatty acid and at most 0.5%by weight of trimer acid, more preferably at most 0.2% by weight ofunreacted unsaturated fatty acid and at most 0.2% by weight of trimeracid, based in each case on the total weight of component (B1).

The dimer acids to be used are obtainable as commercial products.Examples include Radiacid 0970, Radiacid 0971, Radiacid 0972, Radiacid0975, Radiacid 0976, and Radiacid 0977 from Oleon, Pripol 1006, Pripol1009, Pripol 1012, and Pripol 1013 from Croda, Empol 1008, Empol 1012,Empol 1061, and Empol 1062 from BASF SE, and Unidyme 10 and Unidyme TIfrom Arizona Chemical.

Component (B1) generally has an acid number in the range from 190 to 200mg KOH/g.

Component (B2)

According to the invention, component (B2) is at least one C₄-C₁₂diamine. In the context of the present invention, “at least one C₄-C₁₂diamine” means either exactly one C₄-C₁₂ diamine or a mixture of two ormore C₄-C₁₂ diamines.

Examples of suitable components (B2) are selected from the groupconsisting of 1,4-diaminobutane (butane-1,4-diamine;tetramethylenediamine; putrescine), 1,5-diaminopentane(pentamethylenediamine; pentane-1,5-diamine; cadaverine),1,6-diaminohexane (hexamethylenediamine; hexane-1,6-diamine),1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane,1,10-diaminodecane (decamethylenediamine), 1,11-diaminoundecane(undecamethylenediamine) and 1,12-diaminododecane(dodecamethylenediamine).

Preferably, component (B2) is selected from the group consisting oftetramethylenediamine, pentamethylenediamine, hexamethylenediamine,decamethylenediamine and dodecamethylenediamine.

Component (B3)

According to the invention, any component (B3) present in component (B)is at least one C₄-C₂₀ diacid. In the context of the present invention,“at least one C₄-C₂₀ diacid” means either exactly one C₄-C₂₀ diacid or amixture of two or more C₄-C₂₀ diacids.

Examples of suitable components (B3) are selected from the groupconsisting of butanedioic acid (succinic acid), pentanedioic acid(glutaric acid), hexanedioic acid (adipic acid), heptanedioic acid(pimelic acid), octanedioic acid (suberic acid), nonanedioic acid(azelaic acid), decanedioic acid (sebacic acid), undecanedioic acid,dodecanedioic acid, tridecanedioic acid, tetradecanedioic acid andhexadecanedioic acid.

Preferably, component (B3) is selected from the group consisting ofpentanedioic acid (glutaric acid), hexanedioic acid (adipic acid),decanedioic acid (sebacic acid) and dodecanedioic acid.

The invention also provides a process for producing foam particlesaccording to any of claims 1 to 6, comprising the stages of:

-   -   (a) providing a polymer or polymer mixture comprising 85% to        100% by weight of at least one copolyamide, obtainable by        polymerizing the following components:        -   (A) 15% to 84% by weight of at least one lactam,        -   (B) 16% to 85% by weight of a monomer mixture (M) comprising            the following components:            -   (B1) at least one C₃₂-C₄₀ dimer acid and            -   (B2) at least one C₄-C₁₂ diamine,            -   (B) optionally at least one C₄-C₂₀ diacid,        -   wherein the monomer mixture (M) comprises in the range from            45 to 55 mol % of component (B1) and in the range from 45 to            55 mol % of component (B2), based on the total molar amount            of the monomer mixture (M), and the sum total of the            components of (A) and (B) is 100% by weight;    -   (b) impregnating the polymer or polymer mixture with carbon        dioxide, nitrogen or mixtures thereof as blowing agent; and    -   (c) expanding the blowing agent-containing polymer or polymer        mixture under foaming to give foam particles.

In one possible process variant, in stage (b), pellets of the polymer orpolymer mixture are impregnated with gaseous carbon dioxide, nitrogen ormixtures thereof in an autoclave at a pressure in the range of 18 to 25MPa at a temperature in the range from 180 to 250° C. for 1 to 5 hours.

In an alternative process variant, in stage (b), the polymer or polymermixture is melted and the polymer melt is impregnated with carbondioxide, nitrogen or mixtures thereof.

A preferred process comprises the steps of:

-   -   (a) providing a polymer or polymer mixture comprising 85% to        100% by weight of at least one copolyamide, obtainable by        polymerizing the following components:        -   (A) 15% to 84% by weight of at least one lactam,        -   (B) 16% to 85% by weight of a monomer mixture (M) comprising            the following components:            -   (B1) at least one C₃₂-C₄₀ dimer acid and            -   (B2) at least one C₄-C₁₂ diamine,            -   (B) optionally at least one C₄-C₂₀ diacid,        -   wherein the monomer mixture (M) comprises in the range from            45 to 55 mol % of component (B1) and in the range from 45 to            55 mol % of component (B2), based on the total molar amount            of the monomer mixture (M), and the sum total of the            components of (A) and (B) is 100% by weight;    -   (b) melting the polymer or polymer mixture together with 0% to        1% by weight, preferably 0.1% to 0.7% by weight, of a nucleating        agent and impregnating by addition of 1% to 3.5% by weight,        preferably 1.5-2.5% by weight, of carbon dioxide, nitrogen or        mixtures thereof as blowing agent, based in each case on the        polymer or polymer mixture; and    -   (c) extruding the blowing agent-containing polymer melt through        a perforated plate at a temperature between 200° C. and 280° C.        into a pelletizing chamber; and    -   (d) discharging the expanded foam particles from the pelletizing        chamber, wherein water at a temperature of 5 to 90° C. flows        through the pelletizing chamber at a pressure of 0.1 bar to 20        bar above ambient pressure.

It has been found that, surprisingly, the lowest bulk densities are notobtained as expected in the case of maximum amounts of blowing agent,but that an amount of blowing agent of not 30 more than 3.5% by weight,preferably of not more than 2.5% by weight and especially of not morethan 2% by weight leads to a particularly low bulk density. In the caseof an amount of blowing agent of less than 1% by weight, there islikewise a rise in bulk density. The respective proportions by mass arebased here on the total mass of the polymer melt with blowing agentpresent therein.

The optimal amount of blowing agent to be used depends on thethermoplastic polymer used and on the composition of the blowing agent,and is generally between 1% and 3.5% by weight. More preferably, ablowing agent mixture of carbon dioxide and nitrogen is used in amountsin the range from 1% to 3.5% by weight, preferably 1.5-2.5% by weight,based on the polymer or polymer mixture.

The copolyamide used in the aforementioned processes preferably has awater content in the range from 0.05% to 1.0% by weight. The watercontent of the polyamide used can be determined to DIN EN ISO15512:2017-03. If the water content is about 1% by weight, thecopolyamide should be predried.

In the process of the invention, it is possible to add further additivesto the polymers or polymer mixture, such as dyes, pigments, fillers,flame retardants, flame retardant synergists, antistats, stabilizers(for example hydrolysis stabilizers), surface-active substances,plasticizers and infrared opacifiers, in customary amounts.

Suitable infrared opacifiers for reducing the radiative contribution tothermal conductivity are, for example, metal oxides, nonmetal oxides,metal powders, for example aluminum powders, carbon, for example carbonblack, graphite or diamond, organic dyes and dye pigments. The use ofinfrared opacifiers is advantageous particularly for applications athigh temperatures. Particularly preferred infrared opacifiers are carbonblack, titanium dioxide, iron oxides or zirconium dioxide. Theabovementioned materials can be used either individually or else incombination, i.e. in the form of a mixture composed of a plurality ofmaterials. When fillers are used, these may be inorganic and/or organic.

When fillers are present, these are, for example, organic and inorganicpowders or fibrous materials and mixtures thereof. Organic fillers usedmay, for example, be wood flour, starch, flax fibers, hemp fibers, ramiefibers, jute fibers, sisal fibers, cotton fibers, cellulose fibers oraramid fibers. Examples of suitable inorganic fillers include silicates,barytes, glass beads, zeolites, metals and metal oxides. Particularpreference is given to using pulverulent inorganic substances such aschalk, kaolin, aluminum hydroxide, magnesium hydroxide, aluminumnitrite, aluminum silicate, barium sulfate, calcium carbonate, calciumsulfate, silica, quartz flour, aerosil, alumina, mica or wollastonite,or inorganic substances in the form of beads or fibers, for example ironpowder, glass beads, glass fibers or carbon fibers. The average particlediameters or, in the case of fibrous fillers, the length of the fibersshould be in the region of the cell size or less. Preference is given toan average particle diameter or an average length of the fibers in therange from 0.1 to 100 μm, especially in the range from 1 to 50 μm.

Suitable flame retardants are, for example, tricresyl phosphate,tris(2-chloroethyl) phosphate, tris(2-chloropropyl) phosphate,tris(1,3-dichloropropyl) phosphate, tris(2,3-dibromopropyl) phosphateand tetrakis(2-chloroethyl) ethylenediphosphate. Apart from thehalogen-substituted phosphates already mentioned, it is also possible touse inorganic flame retardants in the form of red phosphorus, aluminumoxide hydrate, antimony trioxide, arsenic trioxide, ammoniumpolyphosphate and calcium sulfate, or cyanuric acid derivatives, forexample melamine or mixtures of at least two flame retardants, forexample ammonium phosphate and melamine, and optionally starch and/orexpandable graphite, in order to render the foamed thermoplasticpolymers produced flame-retardant. In general, it has been found to beappropriate to use 0% to 50% by weight, preferably 5% to 25% by weight,of the flame retardants or flame retardant mixtures, based on the totalweight of the blowing agent-containing system.

Prior to the injection of the polymer melt into the pelletizing chamber,it is mixed with the CO₂ blowing agent or a mixture of CO₂ and N₂. Inaddition, it is possible to add a co-blowing agent to the polymer melt.Co-blowing agents used may be alkanes such as ethane, propane, butane,pentane, alcohols such as ethanol, isopropanol, halogenated hydrocarbonsor HCFCs, or a mixture thereof. The sole use of CO₂ or of a mixture ofCO₂ and N₂ as blowing agent is particularly advantageous since these areinert gases that are noncombustible, such that no atmospheres thatpresent an explosion hazard can arise in production. This obviates anyneed for costly safety precautions and greatly reduces the riskpotential in the production. It is likewise advantageous that no storageperiod is required for the products on account of the vaporization ofvolatile combustible substances.

Further advantages arise when one or more nucleating agents areadditionally added to the blowing agent-containing polymer melt.Suitable nucleating agents are especially talc, calcium fluoride, sodiumphenylphosphinate and finely divided polytetrafluoroethylene, eachindividually or else in any desired mixture. The nucleating agent ismore preferably talc. The proportion of nucleating agent based on thetotal mass of the polymer melt is preferably 0.1% to 2% by weight,especially 0.2% to 0.8% by weight.

The increase in the water pressure generally leads to lower bulkdensities and to a more homogeneous product having narrower particlesize distribution.

After leaving the perforated plate, the blowing agent present in thepellets expands and is contacted with a suitable liquid coolant,generally water or an aqueous mixture, so as to obtain expanded foamparticles suspended in water or an aqueous mixture.

The expanded foam particles may be separated from the water stream inthe customary manner, for example by filtering, for example with a meshscreen or curved screen, or typically by means of a continuouscentrifuge.

The expanded foam particles obtained after step (d) typically have abulk density of 5 to 300 kg/m³, preferably of 30 to 200 kg/m³ and morepreferably of 40 to 150 kg/m³.

The expanded foam particles are generally at least approximatelyspherical. The diameter depends on the chosen particle weight of thestarting pellets and on the bulk density produced. But the foamparticles typically have a diameter of 1 to 30 mm, preferably 3.5 to 25mm and especially 4.5 to 20 mm.

In the case of non-spherical, e.g. elongate, cylindrical or ellipsoidal,foam particles, diameter means the longest dimension.

The foam particles may have been provided with an antistat. In apreferred embodiment, this is accomplished by coating.

The expanded foam particles produced in accordance with the inventioncan be used to produce shaped bodies (foams) foamed by methods known tothe person skilled in the art.

For example, the expanded foam particles can be bonded to one another ina continuous or batchwise method with the aid of an adhesive, forexample with polyurethane or epoxy adhesives known from the literature.

Preferably, the foam particles of the invention are thermally welded toone another in a closed mold. For this purpose, the foam particles areintroduced into the mold and temperature is introduced after the moldhas been closed, which results in welding of the foam particles to oneanother to form the foam, preferably having a density in the range from5 to 300 kg/m³. The foams may be semifinished products, for exampleslabs, profiles or sheets, or finished shaped articles having simple orcomplicated geometry. Accordingly, the term “foam” also includessemifinished foam products and foam moldings.

In a very particularly preferred embodiment, the moldings are welded bythe “VARIOTHERM” process known to the person skilled in the art. Thisinvolves compressing the expanded particles in a mold and then heatingup the walls of the mold using a heating medium and holding it at thedesired temperature until the particles have become welded to oneanother. Subsequently, a cooling medium is passed through the walls ofthe mold, which enables rapid cooling of the welded particles in orderto prevent collapse and enable removal of the finished component.

We have now found that moldings made from expanded foam particles basedon PA6.6.36 are surprisingly hard.

These moldings accordingly show good tensile and compressive strengths,sufficiently low compression set and acceptable thermal stability, suchthat they are usable for corresponding applications in the sports andleisure sector, for example as frames for tennis rackets, core materialsfor skis or snowboards, watersports equipment, golf clubs, bicycleframes, toys, model construction, in the packaging or automotiveindustry, and for industrial applications. These moldings are especiallysuitable as core materials of composites, as insulation material inautomobile construction, for example for battery insulation. The shapedbodies are also suitable as core material for sandwich constructions inshipbuilding, aerospace construction, wind turbine construction, andrail and road vehicle construction. They may serve, for example, forproduction of motor vehicle parts, such as trunk bases, parcel shelves,bodywork reinforcements, crash pads and side door trims.

The invention therefore also provides for the use of the foam particlesof the invention for production of foam moldings for the automotiveindustry, wind power industry, building industry, packaging industry,sports and leisure industry, in transport and/or in construction.

EXAMPLES

Raw Materials Used:

-   -   PA6.6/36 Ultramid RX2240, high-viscosity copolyamide from BASF        SE, melting point 199° C. to ISO 3146, density to ISO 1183 of        1.1 g/cm3    -   PA6 Ultramid® B27, nylon-6 from BASF SE    -   Talc IT Extra microscale talc, Mondo Minerals

Test Methods:

Bulk density was determined in accordance with DIN ISO 697:1984-01 byfilling a 500 ml vessel with the expanded particles and determining theweight by means of a balance.

The water content of the polyamide used was determined to DIN EN ISO15512:2017-03.

Example 1: Melt Extrusion

99.5 parts by weight of PA6.6/36 polyamide having a water content of0.134% by weight was melted in a twin-screw extruder (screw diameter 18mm, length/diameter (L/D) ratio=40) at 250° C. and mixed with 0.5 partby weight of talc. Subsequently, CO₂ or a mixture of CO₂/N₂ as blowingagent was metered into the melt, mixed homogeneously and extrudedthrough a perforated plate (hole diameter 1 mm). The perforated platewas electrically heated by means of heating cartridges and kept at atemperature of 280° C. or 240° C. The extruded strand was pelletized byunderwater pelletization (UWP) at a pressure of 1 MPa to give foamparticles having an average diameter of 2 mm and an average weight of 2mg by means of 10 blades secured to a rotating blade ring.

The amounts of the blowing agent added to the polymer melt (based on 100parts polyamide/talc melt), the temperature of the blowing agent-ladenmelt and of the perforated plate, and the bulk density of the resultingfoam particles are collated in table 1.

TABLE 1 Temperature Temperature [C] of the melt [C] of the Bulk CO₂ N₂before the per- perforated density Example [% by wt.] [% by wt.] foratedplate plate [kg/m³] 1.1 1.96 — 251 280 348 1.2 1.96 0.29 251 280 170 1.31.96 0.29 222 240 170 1.4 2.90 0.29 223 240 124

Example 2 and Comparative Experiments: Autoclave Method

20 PA6.6/36 pellets were introduced into a conventional stainless steeltea strainer and placed in a high-pressure autoclave. The autoclave wasclosed, CO₂ or N₂ was injected at a pressure MPa, and impregnation waseffected at a temperature in the range from 180 to 235° C. for 3 hours.Subsequently, the autoclave was decompressed abruptly by opening a ballvalve. After the autoclave had been cooled to room temperature, thefoamed polyamide particles were removed.

The impregnation conditions and foaming characteristics are collated intable 2.

TABLE 2 Impregnation Impregnation Foaming Bulk density Example Polyamidemedium temperature [C.] characteristics [kg/m³] 2.1 PA6/6.36 CO₂ 180 Notfoamed 1100 2.2 PA6/6.36 CO₂ 205 Well foamed 200 2.3 PA6/6.36 CO₂ 210Overfoamed, — many cavities V1 PA6 N₂ 180 Not foamed 1140 V2 PA6 N₂ 205Very lightly foamed, 700 opaque V3 PA6 N₂ 210 Overfoamed, — hollowstructure no particle retention

In the temperature range of 210-250° C., in which the PA 6/6.36 isprocessed in the extruder, viscosity is virtually constant. This leadsto a more stable particle foam. In the case of PA 6, by contrast,viscosity falls significantly within the temperature range mentioned.

The invention claimed is:
 1. Foam particles that have a bulk densitybelow 300 kg/m³ and are based on polyamides, comprising 85% to 100% byweight of at least one copolyamide obtained by polymerizing thefollowing components: (A) 15% to 84% by weight of at least one lactam,and (B) 16% to 85% by weight of a monomer mixture (M) comprising thefollowing components: (B1) at least one C₃₂-C₄₀ dimer acid, and (B2) atleast one C₄-C₁₂ diamine, wherein the monomer mixture (M) comprises inthe range from 45 to 55 mol % of component (B1) and in the range from 45to 55 mol % of component (B2), based on the total molar amount of themonomer mixture (M), and the sum total of the components of (A) and (B)is 100% by weight.
 2. Foam particles according to claim 1, which consistof 85% to 100% by weight of the at least one copolyamide and 0% to 15%by weight of additives.
 3. Foam particles according to claim 1, whichhave a bulk density in the range of 30-250 kg/m³.
 4. Foam particlesaccording to claim 1, wherein component (A) is selected from the groupconsisting of 3-aminopropanolactam, 4-aminobutanolactam,5-aminopentanolactam, 6-aminohexanolactam, 7-aminoheptanolactam,8-aminooctanolactam, 9-aminononanolactam, 10-aminodecanolactam,11-aminoundecanolactam, and 12-aminododecanolactam.
 5. Foam particlesaccording to claim 1, wherein component (B2) is selected from the groupconsisting of tetramethylenediamine, pentamethylenediamine,hexamethylenediamine, decamethylenediamine, and dodecamethylenediamine.6. Foam particles according to claim 1, wherein the at least onecopolyamide has a glass transition temperature (T_(g)) in the range from20 to 50° C., determined according to ISO 11357-2:2014.
 7. Foamparticles according to claim 1, wherein the at least one copolyamide hasa melting temperature (T_(m)) in the range from 150 to 210° C.,determined according to ISO 11357-2:2014.
 8. A process for producingfoam particles according to claim 1, the process comprising the stagesof: (a) providing a polymer or polymer mixture comprising 85% to 100% byweight of at least one copolyamide, obtained by polymerizing thefollowing components: (A) 15% to 84% by weight of at least one lactam,and (B) 16% to 85% by weight of a monomer mixture (M) comprising thefollowing components: (B1) at least one C₃₂-C₄₀ dimer acid, and (B2) atleast one C₄-C₁₂ diamine, wherein the monomer mixture (M) comprises inthe range from 45 to 55 mol % of component (B1) and in the range from 45to 55 mol % of component (B2), based on the total molar amount of themonomer mixture (M), and the sum total of the components of (A) and (B)is 100% by weight; (b) impregnating the polymer or polymer mixture withcarbon dioxide, nitrogen or mixtures thereof as blowing agent to form ablowing agent-containing polymer or polymer mixture; and (c) expandingthe blowing agent-containing polymer or polymer mixture under foaming togive foam particles.
 9. The process according to claim 8, wherein, instage (b), the polymer or polymer mixture which is impregnated withcarbon dioxide, nitrogen, or mixtures thereof as blowing agent, is inthe form of pellets, and the carbon dioxide, nitrogen, or mixturesthereof as blowing agent is/are gaseous, and the impregnating of thepellets with the gaseous carbon dioxide, nitrogen, or mixtures thereofas blowing agent, occurs in an autoclave at a pressure in the range of18 to 25 MPa at a temperature in the range from 180 to 250° C. for 1 to5 hours.
 10. The process according to claim 8, wherein, in stage (b),the polymer or polymer mixture is melted and the melted polymer orpolymer mixture is impregnated with carbon dioxide, nitrogen or mixturesthereof.
 11. A process for producing foam particles according to claim1, the process comprising the steps of: (a) providing a polymer orpolymer mixture comprising 85% to 100% by weight of at least onecopolyamide, obtainable obtained by polymerizing the followingcomponents: (A) 15% to 84% by weight of at least one lactam, and (B) 16%to 85% by weight of a monomer mixture (M) comprising the followingcomponents: (B1) at least one C₃₂-C₄₀ dimer acid, and (B2) at least oneC₄-C₁₂ diamine, wherein the monomer mixture (M) comprises in the rangefrom 45 to 55 mol % of component (B1) and in the range from 45 to 55 mol% of component (B2), based on the total molar amount of the monomermixture (M), and the sum total of the components of (A) and (B) is 100%by weight; (b) melting the polymer or polymer mixture together with 0%to 1% by weight of a nucleating agent and impregnating by addition of 1%to 3.5% by weight of carbon dioxide, nitrogen or mixtures thereof asblowing agent, based in each case on the polymer or polymer mixture, toform a blowing agent-containing polymer or polymer mixture; (c)extruding the blowing agent-containing polymer melt through a perforatedplate at a temperature between 200° C. and 280° C. into a pelletizingchamber, wherein the blowing agent-containing polymer-melt is pelletizedand expanded, thereby forming expanded foam particles; and (d)discharging the expanded foam particles from the pelletizing chamber,wherein water at a temperature of 5 to 90° C. flows through thepelletizing chamber at a pressure of 0.1 bar to 20 bar above ambientpressure.
 12. The process according to claim 8, wherein the at least onecopolyamide used has a water content in the range from 0.05% to 1.0% byweight, determined according to DIN EN ISO 15512:2017-03.
 13. A methodof using the foam particles according to claim 1, the method comprisingusing the foam particles for production of foam moldings for theautomotive industry, wind power industry, building industry, packagingindustry, sports and leisure industry, in transport, and/or inconstruction.
 14. The process according to claim 11, wherein the atleast one copolyamide used has a water content in the range from 0.05%to 1.0% by weight, determined according to DIN EN ISO 15512:2017-03.